Triazole-conjugated spiropyran was synthesized by Cu(I)-catalyzed azide-alkyne cycloaddition and its metal sensing properties were investigated. Color changes were observed upon the formation of metal complex between the spiropyran and Cu2+, which was found to be selective for Cu2+ ions among Co2+, Hg2+, Li+, Mg2+, Ni2+, Zn2+, Cd2+, and Cu2+ ions. Moreover, because of the color change, the complex could be detected by the naked eye. An interesting two-stage metal binding mechanism was observed for the sensing process. First, a metal cation brought the two 1,2,3-triazoles together. Second, the Cu2+ ion was selectively sensed by the conversion of the spiropyran to the merocyanine form. Introduction The design and development of highly selective …show more content…
The free state of SPBT is colorless, and the absorption maximum at 335 nm showed a significant amount of SPBT component. No characteristic absorption maximum was observed in the visible region, indicating the complete absence of the MCBT compound. Upon addition of Cu2+ to the colorless SPBT, it switches to the pink colored MCBT metal complex. The appearance of an absorption band in the visible region at 520 nm envisioned the complexation of MCBT with Cu2+. The ion selectivity can be quantified in terms of the relative intensity based on the absorbance intensities at 520 nm of a solution of SPBT before and after the addition of the metal cations as shown in Figure …show more content…
The controlled experiment of SP with Cu2+ ion (Figure 3) shows 1:1 stoichiometry of Cu2+ and SP [27]. From the previous reports, the triazole group has proven to form an efficient metal ion binding site. With this interest, we planned to investigate the binding sites in SPBT owing to their two binding sites in the same molecule, i. e., 1,2,3-triazole and spiropyran moieties. From the Job’s plot result, we hypothesized that the two triazole units of different SPBT are initially connected by doubly charged metal cation, making necessary arrangement for other two metal cations affecting the activation of the C–O bond, resulting in the conversion of the colorless SP form to the colored MC